Nanoscale printing: better nanowires through 100,000 dpi printing

Researchers from IBM have published a paper describing a technique for taking …

For all the excitement surrounding the potential of nanotechnology, the applications have been few and far between, primarily because working with anything at those size scales is extremely difficult. As a result, mass production of nanoscale devices with consistent properties has been a big hurdle to overcome. IBM and academic researchers in Zurich have collaborated on and published a method that may allow large-scale production by extending a traditional printing method to the nanometer level.

The technique involved is based on gravure printing, in which inks or dyes are loaded into recessed features of a template and then transferred to a substrate that they adhere to. To move this technique to the nanoscale, the researchers took advantage of the lithography techniques developed for the creation of features in silicon wafers. Although it's easy to carve features in silicon, the material is a rigid substrate that many materials normally stick to. To avoid this problem, the team etched the equivalent of a photographic positive image in the silicon; the desired features protruded from an otherwise flat surface. This was used as a template to created recessed features in a flexible synthetic rubber called PDMS.

With the flexible template ready, the issue became loading it with appropriate materials. The authors created a colloidal suspension of gold particles by mixing them with dense detergents. They could force those particles into the recesses in the template by moving a meniscus—a cluster of liquid held together by surface tension—across the PDMS, using a thin glass plate the pull the liquid along. You can get a rough idea of how this works by pulling a drop of water along a Teflon surface using your finger. Due to the dynamics of this meniscus, gold particles would cluster at the trailing surface and settle into the patterns cut into the PDMS.

Nanoscale sun, courtesy of IBM

With the PDMS mold loaded, it was a simple matter to "print" the gold by transferring the pattern to a surface that the particles adhered to. The authors could readily print wires as thin as 60nm across, or ordered grids of individual gold clusters. The image of the sun at left is about 50μm across and printed at a resolution of 100,000 dpi.

Given that the semiconductor industry is already working on 45nm features, it's worth delving into the advantages of this technique, which are significant. To begin with, the silicon should only have to be etched properly once in order to produce many duplicate PDMS templates that could, in turn, be used for multiple print jobs. Different combinations of template material, print material, and substrate could create a wide range of printed material. Finally, the printed materials retain their chemical properties and can be used to template even more exotic materials: the paper describes using arrays of gold clusters to catalyze the formation of silicon nanowires.

Overall, the technique appears to be a potential first step towards the mass production of nanoscale devices. It's not really a breakthrough in scale, as noted, but it appears to bring a far greater flexibility and reliability to the process.